GB2292789A

GB2292789A - Fuel destructor

Info

Publication number: GB2292789A
Application number: GB9417557A
Authority: GB
Inventors: Paul Anthony Gunter
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1994-09-01
Filing date: 1994-09-01
Publication date: 1996-03-06
Anticipated expiration: 2014-09-01
Also published as: GB9417557D0; GB2292789A8; GB2292789B

Abstract

A fuel destructor suitable for use in initiating the destruction of large volumes of inflammable liquid or of slicks on water comprising a buoyant support 1 contained in a plastic housing 8, 9 so as to form an air gap therebetween and so enabling the buoyancy to be reduced by ingress of liquid into the air gap after ignition of the device. The destructor further comprises a thermite pyrotechnic composition 3 housed in a recess 2 of the support 1 and has deflector plate 6 supported above the thermite 3 on pillars 7 to deflect emergent combustion products towards the inflammable liquid and also, in conjunction with the support 1, to form a communication means which can allow inflammable liquid to contact with the hot slag remaining after the combustion of the thermite composition 3 and thereby extending the usefulness of the destructor beyond the combustion time of the thermite 3. <IMAGE>

Description

Fuel Destructor This invention relates to a fuel destructor and more particularly to one suitable for use in the destruction of large volumes of inflammable liquids.

The phrase "burn time" shall hereinafter be taken to mean that period of combustion of a pyrotechnic material during which vigourous burning takes place to eject hot combustion products.

Often when it is required to destroy a substantial volume of inflammable liquid through combustion the ignition of the liquid is attempted by throwing a burning wick or match onto its surface. This method is unreliable and for some oils is totally unsuitable since the thermal energy generated is insufficient to effect their ignition. In this circumstance petrol may be used to prime the ignition of the oil; a practice which, because of the presence of volatile petrol vapour, increases the danger to the person attempting the destruction.

Incendiary devices designed to ignite inflammable liquids on water are currently available, for example that described in the UK Patent Application GB 2 092 275 and that described in the US Patent 4 365 557. Both of these existing devices comprise a deflector plate and a pyrotechnic filling which is designed to be completely consumed during burning. During the burn time of the pyrotechnic each of these devices produces hot combustion products which are deflected by the plate, through vents and across the surface of the liquid in order to initiate its combustion. A disadvantage of these known devices is that they provide for an unreliable ignition of the inflammable liquid particularly in adverse weather conditions since their typical burn times and hence their periods of usefulness are only of the order of two minutes.These burn times may be extended by increasing the amount of pyrotechnic material but this leads to an undesirable increase in both the weight and the physical size of these devices.

Both devices each additionally comprise a floatation means for providing a positive buoyancy so that they can remain afloat during substantially all of the pyrotechnic burn time. However, the device described in GB 2 092 275 is designed to sink since the floatation means is burnt or melted when the majority of the pyrotechnic has been used and therefore has the disadvantage that this device is incapable of supplying useful thermal energy to the surrounding liquid beyond the burn time of the pyrotechnic material.

The device described in US 4 365 557 can be designed either to remain afloat so that the vents are always above the liquid or to sink towards the end of the burn time of the pyrotechnic. However, even when the former design is employed the device has the disadvantage that useful thermal energy cannot be supplied to the liquid beyond the pyrotechnic burn time since the pyrotechnic is completely consumed during this period. Even if thermal energy was to be retained by the device there is no means provided to transfer this energy to the surrounding inflammable liquid.

According to the present invention there is provided a destructor for initiating the destruction of inflammable liquids comprising a pyrotechnic material; a support means for holding the pyrotechnic material; firing means for igniting the pyrotechnic material; vent means for directing the resulting pyrotechnic combustion products and a communication means characterised in that the pyrotechnic material comprises a thermite composition adapted to provide a hot slag after its burn time and in that the communication means is capable of providing for the communication of the inflammable liquid onto the slag.

During its burn time the destructor is therefore capable of supplying thermal energy to the liquid by directing the substantially gaseous pyrotechnic material combustion products. produced during the burn time of the thermite pyrotechnic material, across the liquid surface. Additionally, since inflammable liquid can be communicated to the hot slag which remains after the burn time of the thermite pyrotechnic the device is also capable of initiating and maintaining the combustion of the inflammable liquid beyond the burn time of the pyrotechnic material. The destructor according to the present invention therefore has the advantage that its useful time, during which the combustion of an inflammable liquid may be initiated and maintained, extends beyond that of known devices provided with a pyrotechnic material having substantially the same burn time.

A suitable vent means comprises a deflector arranged to cooperate with the support means to define a gap through which the pyrotechnic material combustion products emerge in a horizontal fan pattern. This arrangement serves to ensure that the combustion products are directed across the surface of the inflammable liquid to increase the prospect of its ignition.

Most preferably the present invention additionally comprises a floatation means capable of providing sufficient positive buoyancy to the destructor to maintain the vent means above the surface of the inflammable liquid for substantially all of the burn time of the pyrotechnic material. This enables the destructor to be used in situations where the depth of liquid is greater than the height of the vent above the base of the destructor, for example such as is the case when dealing with oil spills at sea.

Most usefully the floatation means is adapted to possess a variable positive buoyancy and the communication means is cooperable with the floatation means to introduce inflammable liquid onto the hot slag when the buoyancy is reduced. Initially the buoyancy is such that both the vent means and the communication means are held above the surface of the inflammable liquid so that for substantially all of the burn time of the thermite pyrotechnic material the pyrotechnic material combustion products can be directed across the liquid surface by the vent means. Thereafter, the reduction in the positive buoyancy causes the draught of the destructor to increase to a level where the communication means is orientated so that the inflammable liquid can flow through it and onto the hot slag where it may be burnt.Since the inflammable liquid is prevented from passing through the communication means and onto the pyrotechnic material until near the end of the burn time then the useful time of the destructor is enhanced.

Advantageously the variation in the positive buoyancy of the floatation means is sufficient to permit the lowering of the vent means to the surface of the inflammable liquid. Since the vent means already provides a conduit between the pyrotechnic material and the surroundings then this allows the vent means to also act as the communication means. Thus the need for a separate communication means is eliminated which has the advantages that the manufacturing cost and the complexity of the destructor are both reduced.

The variable positive buoyancy of the floatat;ion means can be achieved by configuring the floatation means to define an air gap into which liquid can flow. This may be done by having a floatation means which comprises a buoyancy element and a container for the buoyancy element, the container and the element being configured to define an air gap therebetween into which liquid can flow. In this way the positive buoyancy of the destructor reduces progressively as the amount of liquid within the floatation means increases, with the absolute amount by which the buoyancy can be reduced being dependent upon the volume of air available for displacement by the liquid.

Usefully, the container is configured to form a barrier to the ingress of liquid having some or all of the portion of the container which is proximal, in use, to the surface of the inflammable liquid formed from a combustible material so that a breach in the container by the combustion of this material is made at some time after the ignition of the destructor. This provides the advantage that the possibility of a premature reduction in the positive buoyancy of the support means is lowered since the ingress of liquid is prevented until after the pyrotechnic is ignited.

Some degree of physical protection for the pyrotechnic material can be achieved by housing substantially all of the material within the support means. In this configuration the walls of support means serve to channel the hot combustion products towards the vent means thereby increasing the area over which the combustion products are dispersed by increasing the velocity with which these products emerge from the destructor. Additionally, by placing substantially all of the pyrotechnic material within the support means the centre of gravity of the destructor is lowered which enhances its stability when floating.

Conveniently, the container is formed from a resilient material, for example an ABS plastics material, and is configured to enclose the remainder of the destructor. Thus the container serves to protect the remainder of the destructor from any physical shock during normal handling and deployment.

In an especially preferred embodiment of the current invention the communication means comprises a wick means having one end disposed towards the base of the destructor, where the base is considered as being that external face of the destructor disposed on the side of the pyrotechnic material opposite the vent means. This enables substantially all of the inflammable liquid to be introduced onto the slag and has the advantage that the destructor may be employed even in situations where the depth of the liquid is too shallow for the destructor to float.

Most preferably both the support means and the flotation means of the present invention are configured to be in abutment with one another and are fabricated from porous material, such as balsa wood, the pores of which are sufficiently small to allow transfer of inflammable liquid to the pyrotechnic material by capillary action.

This has the advantage that the support means and the floatation means can cooperate to act as the wick means of the invention thereby allowing the destructor to be used in both shallow and deep liquid without providing a separate wick means.

The construction of the destructor may be further simplified, providing a consequential advantageous cost saving, by fabricating the support means and the floatation means from the same material so permitting the two means to be made in a single unit.

The firing means preferably comprises a removable igniter having a pyrotechnic portion which is used to initiate the combustion of the pyrotechnic material. As the pyrotechnic portion can be transported separately from the rest of the destructor the risk of accidentally igniting the destructor is reduced.

In the context of the present invention the term thermite is used to mean any metal/metal oxide, metal/metal or metal oxide/metal oxide pyrotechnic composition which burns energetically to leave a metal based slag. For example, a thermite composition comprising a mixture of titanium and manganese dioxide powders bound together using an appropriate quantity of resin binder is particularly suitable for use in this invention. This is because this composition burns to leave a solid slag without passing through a liquid phase thereby reducing the possibility of the slag being ejected together with the pyrotechnic combustion products during the burn time of the pyrotechnic.The binder also serves to moderate the length of the burn time with the quantity chosen to provide a burn time of typically between 15 and 100 seconds for 750g of composition A much longer burn time is likely to result in the production of insufficient heat to light the inflammable liquid and a much shorter burn time would lower the probability of establishing combustion of the inflammable liquid The person skilled in the art will readily appreciate that the exact quantity of binder and the proportions of the two powders are dependent, to some extent, on the properties of the liquid to be destroyed but the two powders are typically mixed in the proportion, by weight, of 8 parts titanium dioxide to 1 part manganese dioxide.

A specific embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing in which: Figure 1 shows an explpded view of a fuel destructor according to the present invention.

Referring now to Figure 1, the fuel destructor comprises a support means and a buoyancy element of unitary design 1 (hereinafter referred to simply as the buoyancy element), constructed from balsa wood, and a container which is made of an upper section 9 and a base section 8, both of which are constructed from ABS plastic. The base section 8 and the buoyancy element 1 form the floatation means of the destructor and are constructed so that together they define an air gap into which liquid may flow. The buoyancy element 1 is formed with a recessed surface 2 such that substantially all of the thermite pyrotechnic material 3 can be housed within the recess. The material 3 comprises 750g of 8 parts titanium dioxide to 1 part manganese dioxide in a resin binder.This is formed into sheets of thermite pyrotechnic which are then placed within the recess 2 but it will be clear to those skilled in the art that the thermite pyrotechnic material in a pressed form may be substituted.

The buoyancy element 1 of the floatation means is further configured to receive four igniter sleeves 4, two each on opposite sides of the element 1. Each sleeve 4 has a first part which extends into and is surrounded by the pyrotechnic material 3 and a second part which is adapted to receive one end of a threaded boss 5.

A sheet steel deflector 6 is supported above and clear of the buoyancy element 1 by means of the support pillars 7 such that the pyrotechnic material combustion products are constrained to emerge from the vent formed between the top of the buoyancy element 1 and the deflector 6 in a 3600 horizontal fan pattern.

This structure is fully enclosed in the base section 8 and the upper section 9 of the container which are bonded together in water-tight connection by chemical welding using a suitable bonding agent such as a 20%:80% mixture by weight of ABS plastic dissolved in butanone to form a resilient housing for the rest of the destructor.

The upper section 9 of the container has access holes 10 which are formed in it in positions corresponding with the igniter sleeves 4 and which are adapted to receive a threaded boss 5. Each boss 5 is maintained in a watertight connection with the upper section 9 and has one end which passes through the hole 10 to be retained in a press-fit engagement within the corresponding ignit;er sleeve 4.

Immediately before use a stick igniter (not shown) can be screwed hand tight into the threaded boss 5 so that a pyrotechnic portion of the igniter extends into the pyrotechnic material 3 and is surrounded by the igniter sleeve 4. This configuration has the advantage that the igniter of the firing means is kept separate from the pyrotechnic material until use thereby further reducing the risk of accidental ignition.

Upon firing the stick igniter, the burning igniter filling ruptures the igniter sleeve 4 causing flames to play upon and ignite the surrounding pyrotechnic material 3 which burns at a temperature of about 18000C for a period of approximately 20 seconds. During this period the hot combustion products from the material are deflected through the vent formed between the top of the buoyancy element 1 and the deflector 6 to initially locally melt the plastic sections 8 and 9 and then to emerge in a 3600 horizontal fan pattern to cause the ignition of the surrounding inflammable liquid. The heat from the burning inflammable liquid and the emergent combustion products causes the base section 8 of the container to melt as far down as the liquid surface thereby exposing the balsa wood floatation means 1 to any unburnt inflammable liquid.

When this destructor is used in liquids with a depth greater than the draught of the destructor, such as is the case for oil spills at sea, buoyancy of the floatation means is such that the destructor floats to support the vent above the liquid surface. As the base section 8 of the floatation means melts to expose the buoyancy element 1 liquid flows into the air space between them, increasing the draught of the destructor and bringing the vent towards the liquid surface.

The destructor is made such that when the maximum amount of air has been displaced by the liquid the vent is at the liquid surface. At this time the vent can now act as a conduit to allow any unburnt inflammable liquid to flow onto the solid slag from the burnt thermite pyrotechnic. This slag is sufficiently hot to ignite this liquid and so is capable of maintaining its combustion after the burn time of the thermite pyrotechnic.

In circumstances where the depth of the liquid is either initially or becomes less than the draught of the destructor then the vent can no longer be maintained at the liquid surface and therefore can no longer act as the communication means. However, the fibrous structure of the balsa wood buoyancy element 1 is such that it is capable of acting as a wick so that any inflammable liquid in contact with it can be drawn up towards the solid slag.

Claims

1. A destructor for initiating the destruction of inflammable liquids comprising a pyrotechnic material; a support means for holding the pyrotechnic material; firing means for igniting the pyrotechnic material; vent means for directing the resulting pyrotechnic combustion products and a communication means characterised in that the pyrotechnic material comprises a thermite composition adapted to provide a hot slag after its burn time and in that the communication means is capable of providing for the communication of the inflammable liquid onto the slag.

2. A destructor as claimed in claim 1 characterised in that it further comprises a floatation means capable of providing sufficient positive buoyancy to the destructor to maintain the vent means above the surface of the inflammable liquid for substantially all of the burn time of the pyrotechnic material.

3. A destructor as claimed in claim 2 characterised in that the floatation means is adapted to possess a variable positive buoyancy and is cooperable with the communication means to introduce inflammable liquid onto the slag as t;he buoyancy reduces.

4. A destructor as claimed in claim 3 characterised in that the variation in the positive buoyancy of the floatation means is sufficient to permit the lowering of the vent means to the surface of the inflammable liquid.

5. A destructor as claimed in claim 3 or claim 4 characterised in that the floatation means comprises a buoyancy element and a container for the buoyancy element, the container and the element being together configured to define an air gap into which liquid can flow.

6. A destructor as claimed in claim 5 characterised in that the container is configured to form a barrier to the ingress of liquid having some or all of the portion of the container which is proximal, in use, to the surface of the inflammable liquid formed from a combustible material.

7. A destructor as claimed in claim 5 or claim 6 characterised in that the container is configured to form a resilient enclosure for the remainder of the destructor.

8. A destructor as claimed in claim 7 characterised in that the container is made from an ABS plastics material.

9. A destructor as claimed in any preceding claim characterised in that the vent means comprises a deflector arranged to cooperate with the support means to define a gap through which the pyrotechnic combustion products emerge.

10. A destructor as claimed in any preceding claim characterised in that the support means is capable of housing substantially all of the pyrotechnic material.

11. A destructor as claimed in any preceding claim characterised in that the communication means comprises a wick means having one end disposed towards the base of the device.

12. A destructor as claimed in claim 11 characterised in that the support means and the floatation means cooperate to form the wick means.

13. A destructor as claimed in claim 12 characterised in that the support means and the floatation means comprise porous material.

14. A destructor as claimed in any preceding claim characterised in that both the support means and the floatation means are fabricated from balsa wood.

15. A destructor as claimed in any preceding claim characterised in that the thermite composition is adapted to produce a solid slag.

16. A destructor as claimed in claim 15 characterised in that the thermite composition comprises titanium and manganese dioxides.

17. A destructor as claimed in claim 16 characterised in that the thermite composition comprises titanium and manganese dioxides in the ratio of 8 to 1.

18. A destructor substantially as herein before described with reference to figure 1 of the accompanying drawings.